Fibre reinforced concrete (FRC) gives engineers greater flexibility in how concrete structures can be designed and reinforced. By incorporating fibres into the concrete matrix, the material can continue to transfer tensile stresses after cracking, providing post-cracking capacity that can be considered as part of the structural design.
This opens opportunities to optimise conventional reinforcement, simplify construction and develop concrete solutions that would be difficult to achieve using traditional reinforcement strategies alone.
However, designing effectively with FRC requires an understanding of how the material behaves beyond first cracking and how that behaviour contributes to the performance of the structural element.
BIM Concrete Studio provides digital tools that can help engineers explore these behaviours, analyse different design strategies and connect structural decisions with the wider BIM workflow.
Understanding Post-Cracking Behaviour
One of the most important differences between conventional concrete and fibre reinforced concrete is what happens after cracking occurs.
Plain concrete has relatively low tensile capacity and, once cracking occurs, its ability to transfer tensile stresses reduces significantly. Conventional reinforced concrete addresses this by using steel reinforcement to carry tensile forces.
Fibres provide another mechanism for transferring stresses across cracks.
As cracks begin to form, fibres bridging the crack can continue to transfer tensile forces. The resulting post-cracking behaviour depends on factors including the concrete matrix, fibre type, fibre dosage, fibre orientation and the interaction between the fibres and the surrounding concrete.
Understanding this behaviour is therefore fundamental when FRC contributes directly to structural capacity.
Moving Beyond Ultimate Strength
Structural design is not simply a question of determining whether a section can resist a particular ultimate load.
Engineers also need to understand how the section behaves throughout the loading process.
Important considerations can include:
✓ Initial stiffness
✓ First cracking
✓ Post-cracking response
✓ Redistribution of stresses
✓ Curvature and deformation
✓ Ductility
✓ Ultimate capacity
This becomes particularly important when fibres are being used to reduce, supplement or potentially replace elements of conventional reinforcement.
Analysing FRC Sections
The FRC Cross Section Tool in BIM Concrete Studio allows engineers to investigate the behaviour of reinforced and fibre reinforced concrete sections using Finite Element Analysis.
Sections can be created using standard rectangular, circular and I-shaped geometries, assembled from multiple geometries, or imported from DXF where more complex shapes need to be investigated.
Materials and reinforcement can then be assigned to the section before generating the FEM mesh and running the structural analysis.
This provides a digital environment for exploring how different combinations of geometry, concrete, fibres and conventional reinforcement influence structural behaviour.
Moment-Curvature Analysis
Moment-curvature analysis provides a particularly useful way of understanding how a concrete section behaves as loading increases.
Rather than looking only at the final resistance of the section, the analysis allows engineers to examine the progression from the initial elastic response through cracking and into the nonlinear behaviour of the section.
For FRC designs, this can provide insight into:
✓ Changes in section stiffness
✓ Crack development
✓ Post-cracking behaviour
✓ Reinforcement yielding
✓ Rotation capacity
✓ Ductility
✓ Structural reserve beyond initial cracking
The FRC Cross Section Tool generates moment-curvature relationships that allow alternative section designs and reinforcement strategies to be investigated and compared.
Exploring Axial Force and Bending
Many structural sections are subjected to combinations of axial force and bending rather than a single isolated action.
M-N interaction domains provide engineers with a way of understanding the combinations of axial force and bending moment that a section can resist.
Using the FRC Cross Section Tool, engineers can investigate these interaction domains while accounting for the behaviour of the concrete, fibres and conventional reinforcement.
This is particularly valuable when evaluating complex structural elements where the loading conditions or geometry make simplified calculations less representative of actual behaviour.
Comparing Reinforcement Strategies
One of the potential advantages of FRC is the opportunity to reconsider how reinforcement is distributed within a structural element.
Depending on the application and design requirements, fibres may supplement conventional reinforcement or enable the amount of traditional reinforcement to be optimised.
Digital analysis makes it possible to compare alternative strategies before committing to a design.
For example, engineers can investigate how changes to fibre performance, conventional reinforcement, section dimensions or material properties affect the response of the section.
The objective is to identify a solution that achieves the required structural performance while making efficient use of materials.
From Structural Analysis to the BIM Model
Structural analysis is only one part of the design process.
Once a solution has been developed, engineers and project teams also need to understand where materials are being used, the quantities required and how the structural solution relates to the wider project.
This is where Model Manager complements the structural analysis workflow.
Model Manager allows IFC models to be viewed and interrogated directly in the browser without requiring specialist BIM software.
Project teams can explore structural elements, inspect model information, isolate components and calculate quantities including lengths, areas and volumes.
This creates a useful connection between the engineering decisions being investigated at section level and the quantities and elements represented within the BIM model.
Connecting Material, Analysis and Model
Used together, FRC Cross Section Tool and Model Manager support different stages of the concrete design workflow.
The FRC Cross Section Tool helps engineers investigate how a section behaves, while Model Manager helps teams understand where the concrete solution is being used within the project and in what quantities.
This can support a more connected approach to:
✓ Structural analysis
✓ FRC design development
✓ Reinforcement optimisation
✓ Material selection
✓ BIM model interrogation
✓ Concrete quantity assessment
✓ Design comparison
Rather than treating material selection, structural analysis and BIM as separate activities, these digital workflows can help bring the information together during the development of the concrete solution.
Designing with Confidence
Fibre reinforced concrete creates opportunities to develop efficient, durable and innovative structural solutions, but achieving those benefits depends on understanding the behaviour of the material and incorporating it appropriately into the engineering design.
Digital analysis provides engineers with a way to investigate that behaviour, compare alternatives and understand the implications of different design decisions before they reach construction.
With FRC Cross Section Tool and Model Manager, BIM Concrete Studio provides a free digital environment for exploring these decisions, from detailed section analysis through to the wider BIM model.
Explore BIM Concrete Studio and discover how digital tools can support your next fibre reinforced concrete design.